1. Field of the Invention
The present invention relates to the art of powder processing of ceramic, glass, or metal articles or component assemblies, and the resultant articles formed thereby. The invention finds particular application in light sources and a process for manufacturing light sources, for example, for manufacturing arctubes used in metal halide lamps. However, the invention is equally applicable to the manufacture of other glass and ceramic articles, as well as to powder metallurgy processes.
2. Discussion of the Art
In powder processing, shaping an article or component is often mediated through the presence of a carrier fluid, which can be a water-based solution, mixture of organic liquids, or molten polymers. Ceramic, glass, and metal powders can be processed with equal facility. The mixture is made to emulate a liquid; a plastic, or a rigid solid by controlling the type and amount of carrier and the conditions (e.g., ambient temperature). The result of the shaping process is a xe2x80x9cgreenxe2x80x9d (i.e., unfired) powder compact that is a solid, but has an internal structure that includes discrete powder particles held together by a binder (usually a component of the carrier fluid). The powder compact is converted to a dense solid (and the microstructure is developed) through subsequent thermal processing to burn out, or pyrolize, the organic phase and densify, or sinter, the inorganic powder. An alternative method for densifying the compact is through thermal processing to eliminate the binder and develop a modest amount of bisque strength followed by infiltration with a melt of a less refractory material. Both sintering and infiltration can be used with equal facility for powder ceramics glasses and metals.
Assemblies are made by joining or bonding two or more manufacturable compacts or components together. It is common to hermetically seal ceramics, e.g., ceramic metal halide arc tubes, with either seal glass or shrinkage fits between the arc tube components (body and plug). The bisque-fired components are typically assembled prior to sintering so that the sintering step binds the components together. The densities of the bisque-fired, first and second components are selected to achieve different degrees of shrinkage during the sintering step. . One known method of bonding powder processed components is described in commonly assigned, published application EP 0 954 011 A1.
Again, by way of example, current two part ceramic metal halide arc tube designs undergo two different presintering cycles in order to join two components with the same solids loading. This can cause complications for optical transmissions. Moreover, it is not uncommon that polishing is subsequently required with shrinkage fits to remove surface defects.
In summary, each of these available techniques has disadvantages and in many cases a required complex shape cannot be made by the available methods. Relying on relative shrink rates in order to form bonds is an exacting art that does not easily lend itself to design alteration and adaptation. Any change in material due to, for example, drifts in production tolerances or changes in suppliers can lead to poor quality components. For example, components can engage too soon in the process and lead to distortion in the final assembly or too late in the process whereby an inadequate seal is formed between the components. Furthermore, designs cannot simply be scaled up and down as required for larger or smaller components. Instead changes must be carefully engineered to determine the impact scaling has on gap sizes and gap closure rates. Additionally, imprecision in the shrink fit process often creates surface defects in shrink fit components. Therefore, shrink fit components often require an additional polishing step.
Other techniques require extra processing steps. For example, glass frits must be properly placed and meltedxe2x80x94an expensive and time-consuming process. Additional processing steps, in turn, require extra processing equipment and floor space. Furthermore, processes that require extra pre-sintering cycles can cause complications for optical transmission.
For the foregoing reasons, a technique for joining or bonding green ceramic components with the same filler loading and therefore the same shrink rates is needed to provide increased design flexibility. Additionally, a technique that reduces the number of processing steps required to make an assembly of components is always desirable and particularly a technique that lends itself to rapid prototyping of new designs.
A suspension adhesive is provided to bond, seal or repair compacts or components. The suspension adhesive comprises a matrix having a melting point and/or glass transition temperature below room temperature, and matching particulate filler. The particulate filler is dispersed through the matrix in a volume fraction substantially matching the volume fraction of the particulate filler associated with the components.
Additionally, a method for bonding, sealing, repairing or modifying components comprised of particulate filler has been developed. The method comprises the steps of combining an organic matrix with an amount of the particulate filler, forming a suspension adhesive having a volume fraction of particulate filler, substantially matching a volume fraction of particulate filler found in the components, applying an appropriate amount of the suspension adhesive to at least one surface of the components, treating the components to remove binder material associated with the components and to remove the organic matrix, and sintering the components to bond, seal, or repair the components.
A formulation of a low molecular weight polymer or oligomer based binder of a rubbery nature is sued in another embodiment of the invention. A ceramic powder having substantially the same concentration as the green or presintered ceramic parts to be joined is suspended in the binder with an optional dispersant and a high molecular weight additive. The oligomeric polymer in the suspension allows for desired rheological and thermal properties leading to high quality seals.
The adhesive and method for bonding, sealing, repairing or modifying components is used to make a light source. The light source comprises a first component and a second component bound thereto with a suspension adhesive to form an initial assembly. The initial assembly is treated to remove any binder or organic matrix from the initial assembly. The components and adhesive are subsequently sintered to form the component assembly.
One advantage of the present invention resides in the ability to rapidly prototype new designs.
Another advantage of the present invention stems from an ability to produce new assemblies or parts in low volume without incurring prohibitive tooling costs.
Yet another advantage of the present invention is found in a reduced number of production steps, reducing production time, resources and cost.
A further advantage of the present invention is improved product quality and yield resulting from a reduction in product handling and temperature cycling.